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<head>
  <meta charset="UTF-8">
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  <title>Document</title>
</head>
<body>
  
  <script>
    let grade=Number (prompt('请输入您的分数'))

    if(grade>=90){
      alert(`您的等级为A`)
    }else if(grade<90&&grade>=80){
      alert(`您的等级为B`)
    }else if(grade<80&&grade>=70){
      alert(`您的等级为C`)
    }else if(grade<70&&grade>=60){
      alert(`您的等级为D`)
    }else{
      alert(`您的等级为E`)
    }



  </script>
</body>
</html>